Design Specification
Environmental Detection Device (EDD)

Christian Doyle, Joshua Wagner, and Logan Howell



















Owner: Christian Doyle

June 9th, 2022

Version 1.0

Revision History Block

Table of Contents

1: Overview / Introduction        5

1.1: System Overview        6

2: Requirements        7

2.1: Measuring capabilities        7

2.2: Features        7

2.3: Physical Attributes        8

3: System Architecture        9

3.1: Hardware Architecture        9

3.11: Microcontroller/Bluetooth module        11

3.12 Sensors        11

3.121 Multichannel gas sensor        11

3.122 VOC sensor        12

3.123 O2 sensor        12

3.124 Temperature sensor        12

3.2: Firmware Architecture        13

4: System Design        14

4.1: Hardware Design:        14

4.2: Software Design:        14

4.3: Human Interface Design:        14

5: Project Bill of Materials (BOM)        16

6: Ethical Considerations        17

7: References        18

8: Errata        20

1: Overview / Introduction

The goal of this project is to design and create a wearable, low-cost, battery-powered & Bluetooth-enabled device that uses sensors to measure and record exposure levels of a variety of hazardous gasses and compounds that first responders encounter during emergency scenarios.

In this document, one can find a description and diagram of the high-level architecture of this device, as well as that of its low-level components. This document will also describe the architecture of the firmware used by the device’s microcontroller and the human interface which the device uses.

This document is designed to be a resource for any person interested in the architecture and functionality of the Environmental Detection Device or any person looking to implement the device, and in essence can serve as a training guide for those people.

        With this specification, one will be able to understand the architecture of the Environmental Detection Device, ensure that it meets their requirements, and have a reference for future projects that accomplish a similar task.

This document should be read by someone with a technical background who has experience developing and working with PCBs and device firmware, implementing Bluetooth, and a general knowledge of engineering concepts.

1.1: System Overview

First responders, such as firefighters, have frequent encounters with a variety of gasses and toxins during emergency situations. Many of these are known to be dangerous to humans for various reasons, such as being lung/eye irritants and being carcinogenic. These toxic gasses are especially dangerous considering many of them are colorless and\or odorless. As a result of these risks firefighters have a 9% higher chance of being diagnosed with cancer and a 14% higher chance of dying from cancer when compared to the general population according to research from the CDC and NIOSH. Therefore, it is important to have a device to monitor what these first responders are exposed to so that they can be properly treated and steps can be taken to reduce their exposure. The Environmental Detection Device fulfills this need by measuring the levels of a variety of gasses and toxins and communicating these values to a system in which they can be monitored, via Bluetooth.

With the Environmental Detection Device we will be able to infer the concentrations of:

2: Requirements

2.1: Measuring capabilities

• Ability to measure the concentrations of gasses that first responders are most commonly exposed to (see 1.1: System Overview for list of gasses)

• Gasses that are already naturally present in the air, such as carbon dioxide, can also reach levels that are unsafe for humans

• Ability to measure the concentrations of airborne toxins that first responders are most commonly exposed to (see 1.1: System Overview for list of airborne toxins)

• Various airborne contaminants are released into the air from the burning of household materials. These contaminants include can be toxic and/or carcinogenic

• Ability to measure oxygen levels

• As the levels of other gasses and airborne toxins increase, the levels of oxygen in the air start to decrease which can lead to hypoxia

• Ability to measure temperature

• First responders can be exposed to intense temperatures, such as in a fire

2.2: Features

• Ability to transmit gas and toxin levels via Bluetooth
• Battery life of 8 to 10 hours

• Rechargeable

• Ability to alert the wearer via warning LEDs when the air has become unsafe

• Three different LED colors for three different levels of safety based on concentrations of gasses and airborne contaminants

• Green - Normal state. There is a safe level of airborne contaminants
• Blue - Caution state. There is a potentially hazardous level of airborne contaminants. User(s) should take caution and leave the area if practical.
• Purple - GTFO state. There is a very high concentration of airborne contaminants. User(s) should leave the area immediately.  

• On/Off Switch

2.3: Physical Attributes

• Small in size
• Wearable
• Lightweight

3: System Architecture

3.1: Hardware Architecture

 Hardware Diagram of Environmental Detection Device

Front and back of PCB board

High-level diagram of Environmental Detection Device

The diagram above shows the high-level architecture of the Environmental Detection Device. The microcontroller, with our custom firmware, communicates with the gas and toxin sensors and sends the measured values via Bluetooth so that they can be recorded or monitored in real-time.

The sensors are connected to the microcontroller, which is where they communicate the gas values. The microcontroller also has a Bluetooth module so it can transmit these values to another device. All components are connected to the switch, which connects to the battery pack through a 5V buck converter. This acts as the power supply. Power may also be supplied through the USB port on the microcontroller.

3.11: Microcontroller/Bluetooth module

        The Arduino Nano 33 IoT acts as our Bluetooth microcontroller for the device. The main function of this microcontroller is to read gas/toxin values from the sensors and compare them to specific threshold values. Depending on whether the read gas/toxin levels exceed one or more of the specified thresholds, the microcontroller may signal to the RGB LED to change color and indicate a warning or GTFO situation. This microcontroller is also responsible for sending gas/toxin levels, as well as the measured temperature, via Bluetooth to an external receiver.

3.12 Sensors

3.121 Multichannel gas sensor

For the multichannel gas sensor used in the device, we used the Adafruit MiCS5524 multi gas sensor in our integration. This multi gas sensor can detect CO, C2H6OH(Ethanol), H2, NH3(Ammonia), CH4(Methane). Platforms supported: Arduino.

3.122 VOC sensor

For the VOC/eCO2 sensor, we used the Grove SGP30 sensor. The input voltage for the sensor is 3.3-5V. The output range is 0-60000ppb for TVOC, and 400-60000ppm for CO2eq. Sampling rate for both substances is 1HZ. Platforms supported: Arduino and Raspberry Pi. Default I2C address: 0x58.

3.123 O2 sensor

For the O2 sensor in the device, we used the Grove MIX8410 sensor. The input voltage for the sensor is 3.3-5V. The temperature range is -20 oC~50 oC. The sensitivity is 0.05~0.15 mA(in air). It takes 20 minutes for the sensor to preheat. It can measure between 0% and 25% oxygen. The sensor’s “detect life” is listed as 2 years. Platforms supported: Arduino and Raspberry Pi.

3.124 Temperature sensor

For the temperature sensor in the device, we used the TMP36 sensor. This sensor outputs an analog voltage that is proportional to the ambient temperature. The voltage input range for this sensor is between 2.7V and 5.5V. The output range for the sensor is between 0.1V (-40°C) and 2.0V (150°C) with an accuracy of 2°C.

3.2: Firmware Architecture

The diagram above shows the firmware architecture of the Environmental Detection Device. The gas levels and temperature are communicated to the microcontroller. The firmware checks the values of all these gasses/toxins to see if they are within a range that should trigger the GTFO light or the warning light, which is done by sending a signal from the microcontroller to the RGB LED. If they are, then this will trigger the GTFO light or warning light depending on which threshold has been exceeded. If not, then the firmware will trigger the normal “on” state light. Lastly, the firmware will transmit the gas/toxin values and temperature via Bluetooth. This entire procedure will be performed repeatedly at a specified interval.

4: System Design

4.1: Hardware Design:

One of the primary objectives of the hardware design is to make the device as compact as possible. The only hard restraint is that it must be wearable.
Components planned for use are as follows:

• Arduino Nano 33 IoT - Bluetooth microcontroller
• TMP36 - Temperature sensor
• Grove MIX8410 - Oxygen sensor
• Grove SPG30 - VOC sensor
• Adafruit MiCS5524 - Multichannel gas sensor
• RGB LED
• On/Off switch
• 2 x 3.7V 1000mAh LiPo batteries
• Anmbest 5PCS 2S 7.4V 8.4V 8A 18650 Charger PCB BMS Protection Board for Li-ion Lithium Battery Cell
• Female barrel jack - Charging port
• TSR 1-2450E - 5V Step-Down Buck Converter

The device has an on/off switch and USB charging port. The RGB LED is the only data indicator on the hardware itself giving simple data based on the highest concentration of detected gas in the area.

4.2: Software Design:

Software is written with Arduino. The objective of the software is to relay the detailed information from the sensors through Bluetooth to a receiver to display them in detail. Additionally, the software will work in tandem with the microcontroller to monitor gas levels and control a RGB LED based on the highest concentration of all measured substances.

4.3: Human Interface Design:

For the interface, we have a simple communication method to avoid confusion in intense emergency situations. The device has a RGB LED that shines in different colors based on the highest concentration of detected gas in the area. An “On/Off” switch is placed in a convenient spot on the device and the “On” status of the device can be determined by the presence of light being emitted from the LED. There are three basic levels communicated from the LED: safe, caution, and GTFO. The system is intended to be worn somewhere on the user’s body where it can sample air around the user. The system is not intended to be used in liquid environments. For detailed sensor information, the device can be paired with Bluetooth to a display. Subject to range of the Bluetooth. The device will only require knowledge of the color code by the wearer.

5: Project Bill of Materials (BOM)

List of Required Components:

• Arduino Nano 33 IoT - Bluetooth microcontroller - $18.40 ($3.44 shipping)
• TMP36 - Temperature sensor - $8.99 (for 5)
• Grove MIX8410 - Oxygen sensor - $54.90
• Grove SPG30 - VOC sensor - $17.50 ($5 shipping)
• Adafruit MiCS5524 - Multichannel gas sensor - $14.95 (for 2)
• RGB LED - $7.96 (for 100)
• On/Off switch - $4.68
• 2 x 3.7V 1000mAh LiPo batteries - $9.34 / each - $18.68
• Anmbest 5PCS 2S 7.4V 8.4V 8A 18650 Charger PCB BMS Protection Board - $10.49 (for 5)
• Female barrel jack - Charging port - $6.99 (for 12)
• TSR 1-2450E - 5V Step-Down Buck Converter - $4.17
• PCB boards - $58.10 (for 3)
• Multicomp Pro 10 ohm SMD resistor - $5 (for 1000)
• Taiyo Yuden 0.1uF SMD capacitor - $0.125
• Yageo surface mount chip 680 ohm resistor - $0.012 (for 10)

Total cost: $239.38 (including extra parts)

Cost of parts: $158.30

6: Ethical Considerations

Due to the situations this product is intended for use in, it is imperative that there is no significant error in detection or in communication of the work, as it could lead to the injury or even death of the users. The best way to mitigate this possibility is to perform thorough testing of the device, and in the event that the device should fail: make it obvious to the user that something is wrong with the machine. This could be done through a failsafe or possibly redundant sensor testing and reporting discrepancies. At the least, a lack of measurement variation for a period of time could be detected and a warning given.

As a secondary concern, failure of the measurement system could result in a responder being unable to properly file for medical care based on the substances they have been exposed to. The mitigation being the same as above: don’t have the device fail.

7: References

• Sponsor Questions:

• https://docs.google.com/document/d/17Z0Y0VPMLCdM1HKGYRVCt8_yY4B1ONhXSj6AFqROQMs/

• Project Proposal:

• https://docs.google.com/document/d/1ZKVTLYLvTAdvSGlSv5viJmjEIwO97yDM_sbzbKjGKyI/
  

• Bluetooth Specifications List:

• https://www.bluetooth.com/specifications/specs/

• Multichannel Gas sensor:

• https://wiki.seeedstudio.com/Grove-Multichannel_Gas_Sensor/

• Adafruit Multichannel Gas Sensor

• https://www.adafruit.com/product/3199

• VOC and eCO2 sensor:

• https://wiki.seeedstudio.com/Grove-VOC_and_eCO2_Gas_Sensor-SGP30/

• O2 sensor:

• https://wiki.seeedstudio.com/Grove-Gas_Sensor-O2-MIX8410/

• Gas exposure effects:

• https://inspectapedia.com/indoor_air_quality/Toxic-Gas-Exposure-Effects.php

• TMP36 specs:

• https://www.analog.com/media/en/technical-documentation/data-sheets/TMP35_36_37.pdf

• Microcontroller:

• https://store-usa.arduino.cc/products/arduino-nano-33-iot

• Firefighter cancer statistics:

• https://firefightercancersupport.org/resources/faq/

• NFPA standards website

• https://www.nfpa.org/Codes-and-Standards/All-Codes-and-Standards/List-of-Codes-and-Standards

• Bluetooth website

• https://www.bluetooth.com/learn-about-bluetooth/key-attributes/range/

• Multicomp Pro Resistor

• MCWR04X10R0FTL - Multicomp Pro - SMD Chip Resistor, 10 ohm, ± 1% (newark.com)

• Taiyo Yuden capacitor

• TMK105B7104KVHF - Taiyo Yuden - SMD Multilayer Ceramic Capacitor, 0.1 µF, 25 V (newark.com)

• Yageo surface mount resistor

• RC0402FR-07680RL - Yageo - Surface Mount Chip Resistor, Thick Film, RC Series (newark.com)

8: Errata

• The original goal was for the Environmental Detection Device to be able to differentiate between certain gasses such as carbon monoxide, ammonia, hydrogen, and methane. However, upon closer inspection of the datasheet for our multi gas sensor, we found that it does not do this. We explored similar gas sensors and found that there are currently no sensors available (in our price range) that can differentiate between these gasses or even detect whether a specific gas is present in the first place. We met with a representative from Arrow Electronics and with discussion and brief research, we concluded that it would require too much time (and likely too much money) to come up with a reasonable method to differentiate between these gasses. In our final prototype, the EDD will be able to tell the levels of gasses assuming the present gas is known, and it will be able to provide an alert if any of these exceeds a given “safe” range, however it will not be able to accurately differentiate between these gasses or detect the presence of a particular gas. Regardless, the oxygen sensor and carbon dioxide + total VOC sensor are able to accurately differentiate between the gasses they detect, so we’ll be able to provide accurate concentrations for those.